The Difference Engine, though it was not really completed, was the first machine to be worthy of being called a computer. Like todays computers, the Difference Engine had a store--that is, somewhere where data could temporarily be stored for subsequent processing--and was designed to print its output onto a soft metal, which could then be used to make a printing plate. The first general-purpose computer was accurate to 31 decimal places, and when the engineering team finished building a replica of what would become the worlds first computer printer, they were stunned by its sophistication and featureset. By most definitions, the Difference Engine was the true computer, as understood today--or it would be, had the mathematician in England not once again encountered problems with its implementation. The basic design for the first general-purpose computer, which consisted of more than 50,000 components, included input devices, such as punched cards, that contained the operational instructions, and the storage of 1000 numbers, of which was 50 decimal digits long. The first computer to achieve Turing completion, and possessing these four essential features of our present computers, was ENIAC , which was developed covertly by the U.S. Army, and was first commissioned to operate at the University of Pennsylvania on Dec. 10, 1945, for use in studying the feasibility of a hydrogen bomb. The milestone computing project that was to become known as the Electronic Numerical Integrator and Computer , was the first fully electronic computer capable of performing complicated calculations successfully and with astounding speed. As ENIAC was first conceived of and programmed for the computation of ballistics research for the U.S. Army in World War II, the project was kept hidden from the public until 1946. When the groundbreaking computer project began, those involved with the top-secret venture simply called it Project PX. For one thing, since ENIAC operated in military secret, it was virtually unknown outside of computer circles. Until 1955, when ENIAC was knocked out of commission by a lightning bolt, ENIAC performed computations related to developing the hydrogen bomb and other military projects. ENIAC underwent its first complete test in November 1945, with computation problems arising from H-bomb products fed into it. Designed by John Mauchly and J. Presper Eckert, ENIAC was the fastest computing device of its day, capable of performing 5,000 additions per second, but since it had no internal memory, it had to be programmed by hand for each new set of calculations. Compared with other computers performing similar practical functions, ENIAC was a strange bird, from a technical standpoint. As far as the hardware itself was concerned, there had been other partially electronic computing devices prior to it, but ENIAC is recognized as being the first completely electronic, programmable machine. Although only the first of many models, the Z1 computer led to some significant developments. The first computer, the UNIVAC, was the first mass-produced, functional commercial computer in history, and opened the door to the larger commercial market. Although only 46 first-generation UNIVACs were built, the machine made waves in 1952 when, on national television, it correctly predicted the presidential election outcome between a competing candidate, Eisenhower, and Stephenson. Physicist Dr. John Mauchly and electrical engineer J. Presper Eckert -- the duo that built the UNIVAC -- worked with a team from the University of Pennsylvanias Moore School of Electrical Engineering to design the first UNIVAC computer. The first UNIVAC computer was designed and developed by Dr. John Mauchly and J. Presper Eckert - who had also invented the electronic numerical integrator and computer - between 1946 and 1951. By late 1941, Mauchly was teaching at Penns and discussing ideas for computing with Eckert. Iowa State Professor John Atanasoff attended Mauchlys lecture in December 1940, and the two began to correspond and discuss potential for electronic computers thereafter. With help from graduate student Clifford Berry and several research grants, Atanasoff built a prototype ABC computer, which was demonstrated in October 1939. Completely tested during World War II, the Atanasoff-Berry Computer, also known as ABC, was the first digital electronic computer in the world. The Colossus was the worlds first programmable electronic digital computer. In addition to its obvious significance in being considered by many to be the first personal computer, Edmond Berkeleys invention established at least half a dozen world records . Edmund Berkeleys first personal computer, the Simon electronic brain, sold for only $600 in 1950 -- a price tag that seems just as unheard of today as it did more than 70 years ago. Edmund Berkeleys invention also introduced to the public the technical principles of binary arithmetic, computing logic, and automated computation. Shortly thereafter, in 1949, Edmund Berkeleys wrote one of the first books about electronic computers aimed at the general public. He had proposed the first computer, a machine that he called the "Differential Engine", in 1822--the earliest computers were about the size of houses, could store programs, were powered by steam, and even printed results. At the end of the Second World War - during which he helped crack the Enigma codes for the Nazis encoded messages - Turing created one of the earliest computers resembling the present-day one, an automatic computing engine that, as well as being digital, was programmable; that is, it could be used to do a lot of things just by changing a program. ENIACs relied on a decimal system with 10 digits, instead of the binary one-and-zero system used by practically every subsequent computer, including those developed by Eckert and Mauchly. The milestone computer design was, to put it bluntly, a gigantic brain, measuring 1,800 square feet and weighing almost 30 tons.